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March 21, 2012

Geologic Map Reveals Io’s Otherworldly Volcanoes

by editor

A team of scientists led by Arizona State University has produced the first complete geologic map of Jupiter´s moon, Io. Published by the US Geological Survey, the new map reveals geologically unique features, volcanoes, and lava flows as well as some relative ages of the moon.

Galileo first discovered Io more than 400 years ago. Io is the largest and innermost moon to orbit the planet Jupiter and has been the subject of many scientific studies as well as intense observation. Existing research has taught us about the orbital route taken by Io around Jupiter as well as its gravitational relationship to the other moons. As Io travels around sister moons Europa and Ganymede and Jupiter, the rocky crust that makes up the moon´s surface rapidly melts and flexes. This flexing creates a great amount of heat within the moon´s core and is therefore vented through the moons volcanoes.

David Williiams is a faculty research associate in the School of Earth and Space Exploration at ASU and led the six-year research project to geologically map Io.

“One of the reasons for making this map was to create a tool for continuing scientific studies of Io, and a tool for target planning of Io observations on future missions to the Jupiter system,” said Williams in a press release explaining his research.

His highly detailed and colorful map reveals a number of volcanic points and features, such as: Paterae, or caldera-like depressions, lava flow fields, a various amount of plume deposits, and volcanic domes called “tholi”. There is one feature missing from these images, however.

Says Williams: “Io has no impact craters; it is the only object in the Solar System where we have not seen any impact craters, testifying to Io´s very active volcanic resurfacing.”

These images also revealed another peculiar fact: Although Io is more than 25 times more volcanically active than Earth, the majority of long-term surface changes resulting from volcano eruptions effect less than 15 percent of the surface. Most of these changes are in the form of lava flow fields and paterae.

“Our mapping has determined that most of the active hot spots occur in paterae, which cover less than 3 percent of Io´s surface. Lava flow fields cover approximately 28 percent of the surface, but contain only 31 percent of hot spots,” says Williams. “Understanding the geographical distribution of these features and hot spots, as identified through this map, are enabling better models of Io´s interior processes to be developed.”

To build this map, Williams used four distinct image mosaics captured by NASA´s Voyager 1 and 2 missions as well as the Galileo Orbiter. He then combined this data with existing surface material data to determine size and location. He then correlated his map with locations of existing hot spots on Io´s surface.

“Because of the non-uniform coverage of Io by multiple Voyager and Galileo flybys, including a variety of lighting conditions, it was absolutely necessary to use the different mosaics to identify specific geologic features, such as separating mountains and paterae from plains, and separating the colored plume deposits from the underlying geologic units,” says Williams.

Completing this USGS-published map provides other scientists with a way to consider new hypotheses about geological evolution as well as a better way to understand existing volcanic activity.

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Image Caption: Galileo spacecraft image of Io. The dark spot just left of center is the erupting volcano Prometheus. Whitish plains on either side of it are coated with volcanically emplaced sulfur dioxide frost, while yellower regions are encrusted with a higher proportion of sulfur. Credit: NASA/JPL/University of Arizona